This invention relates to modular handling systems as used for industrial applications for transporting or assembling workpieces or for performing any kinds of operations on such workpieces. Handling systems of the prior art have already used linear drive modules for performing linear displacements of further modules of the handling systems or of tools, particularly gripping tools for grasping workpieces and transporting or otherwise displacing or rotating same. In the prior art systems, linear drives have been used with pneumatic drive systems comprising a piston travelling within a cylindrical bore and being subjected to pneumatic pressure on either side of the piston, resp. The piston of prior art systems was connected on both sides with a flexible belt, travelling through pressure-tight lead-throughs of the linear drive and being returned by means of deflection rollers over the longitudinal lateral side of the linear drive. The flexible belt carried a carriage, travelling on the outside of the linear drive in an opposite direction of the piston.
However, one main drawback of prior art systems is that any module of the handling system had to be supplied individually with electrical energy, electrical control signals and operating fluid, e.g. compressed air. Thus, prior art handling systems had to be equipped with a plurality of cables, wires, and tubes. The necessity of individual wiring and tubing of all modules has reduced the freedom of displacement and rotation of the modules of the handling system.
Another drawback of prior art systems was that control valves, being arranged on the front end and rear end of a linear drive, resp., for controlling pressure on either side of the piston where subject to fluctuations resulting from variations of ambient conditions, e.g. ambient temperature. Prior art modular handling systems have used linear drives with so-called displacement-servo-valves generating a signal corresponding to the axial displacement of a valve spool and feeding back this signal to a driving stage which , in turn, operates the spool. Displacement-servo-valves of this type have an output pressure vs. operating current characteristic with the shape of a stepped function wherein output pressure is zero for low operating currents and rises quickly up to the maximum value of output pressure if a certain operating current threshold value is surpassed. When combining two such valves, the operating point of the system is defined by the intersection of two such characteristic curves, the two curves being symmetrical to each other because of the symmetrical arrangement in two cylinder heads of a linear drive. Therefore, the intersection of the two curves is within the rising portion of the stepped curve which means that the two curves intersect with an intersection angle of almost zero. If there is a fluctuation of the curves, e.g. due to fluctuation of the ambient temperature, the intersection point of the two curves will vary substantially in the ordinate direction if the curves slightly fluctuate in the abscissa direction. Therefore, output pressure of both displacement-servo-valves will vary substantially and, thus, destablize the operation of the entire handling system.
It is, therefore, a first object of the present invention to provide for a modular handling system in which the need for cabling and wiring is drastically reduced.
It is, further, another object of the invention to provide for a modular handling system in which the stability of the entire system is greatly enhanced.